The invention relates to a vulcanisation mould for the manufacture of technical rubber products, in particular for the manufacture of vehicle tires, comprising a plurality of venting bores in each of which there is provided a blocking member, which at least substantially blocks the penetration of blank material.
Vulcanisation moulds of this kind are, for example, known from U.S. Pat. No. 4,347,212 or from the German patent specification 195 43 276 C1.
The purpose of the venting bores, of which several thousands can be provided in one vulcanisation mould, is to ensure a problem-free venting of all regions of the vulcanisation mould provided with tread pattern forming webs in order to ensure that the tire blank can accurately contact the form-giving tools or webs of the vulcanisation mould from the inside during the inflation process and that such accurate contact against the mould is not hindered by air inclusions.
An undesired disadvantage of the existing vent bores lies in the fact that rubber enters into these bores, which normally have a diameter of 0.7 to 1.5 mm, and the so-formed shoots give the finished tire a brush-like or hedgehog-like appearance. Various techniques are admittedly known to remove these undesired shoots; however, all these techniques cause extra work and considerable costs.
In order to avoid the undesired shoots it is known to insert valves into the venting bores which are closed by the approaching surface of the blank and which open again during demoulding. The disadvantage of valves of this kind which have hitherto been used in tire vulcanisation moulds lies above all in the fact that they are complicated as a result of their multi-part construction and that a coil spring is required to ensure a defined closing and opening process, with the coil spring always having, as far as possible, the same characteristic for the large number of valves that are required. The extremely small dimensions of these valves make it more difficult to ensure practically identical characteristics.
The object of the invention is to provide a ventable vulcanisation mould with blocking members which are particularly simple and thus economically designed, which can be installed and removed without problem and rapidly and which ensure a high operational reliability.
This object is satisfied in accordance with the invention essentially in that each blocking member includes a central body, in particular a pin-like central body, which can be fixed in the respective vent bore in force-locked manner, and also a sealing part connected to the central body, with the sealing part having a surface region at the inner side of the mould and substantially flush with it, which is provided with at least one aperture and forms, together with the mould-side end face of the central body at least one flowpath for the air, which is pronouncedly angled following the aperture.
Through the special design of the blocking member, which can be of one-piece or two-piece construction, it is possible to stop the blank material which meets the blocking members without any movable elements and simply as a result of the guidance of the air flow and to prevent any form of disturbing penetration of blank material into the air discharge passages that are formed, which would lead to shoots at the finished product, which in turn has the consequence that on opening the mould no rubber material remains in the specially formed air discharge passages and could block the latter.
The absence of any movable elements, such as are present when using valves in the form of movable valve stems, leads to a high operational reliability and, above all, to the fact that no damage arises during cleaning of the moulds, which is frequently effected by blasting them with ice crystals, which could make the blocking members unsuitable for use. A further advantageous consequence of the design of the blocking members in accordance with the invention is the fact that the mould cleaning cycles can be substantially extended because of the largely avoided danger of blocking members becoming ineffective through contamination.
When the blocking member of the invention is of two-part construction, a resilient latching of the sealing part to the central body preferably takes place. For this purpose, parts of the clamping limbs which are intended for the fixation of the central body in the mould bores and which are connected to the disc-like blocking surface are cranked inwardly in the form of coupling lugs and engage behind support projections on the central body so that a snap-in latch connection is provided.
The blocking members formed in accordance with the invention can be simply and rapidly positioned accurately in bores of the respective mould, since for this it is only necessary to press the blocking members into the bores and the end position is achieved when the edge of the disc-like blocking surface comes into contact with the wall of the mould.
The blocking member of the invention accordingly operates in the manner of a nozzle with a specially shaped air guidance which prevents the formation of mould shoots, for which purpose, on the one hand, the minimal dimensions of the existing air guidance channels and, on the other hand, the angled shape of these air guidance channels is characteristic.
In accordance with a second embodiment variant, the blocking member is movable at least in the sense that it has an elastically deformable surface region at the inside of the mould. This surface cooperates in an at least substantially sealing manner with the central body on being loaded by the surface of the blank. The blocking member thus forms a two-part valve with the central body in accordance with this embodiment.
In other words, the object is satisfied in accordance with the invention in a second basic way by a vulcanisation mould for the manufacture of vehicle tires having a plurality of venting bores, in each of which a valve is mounted and designed in such a way that it is at least substantially closed by the approaching surface of the blank and is opened again on demoulding, with the special characteristic that each valve is of two-part design and includes a central body, in particular a pin-like central body, which can be fixed in the respective venting bore, and also a sealing part which is releasably connected to the central body and which has at least one elastically deformable surface region disposed at the inner side of the mould, which cooperates in an at least substantially sealing manner with the central body on being loaded by the surface of the blank.
Even though a movement of the surface region of the blocking member disposed at the inner side of the mould occurs in the sense of an elastic deformation thereof in this embodiment variant in order to achieve a complete sealing and therefore a valve function, the degree of movement is relatively small and cannot be compared with the previously known embodiments with valve tappets. With this second embodiment variant, practically all advantages of the first embodiment variant can thus be achieved, with, however, the said first embodiment variant in accordance with FIGS. 1 to 3 representing the best embodiment in the opinion of the applicant.
Not only is a substantial simplification of the construction of the valve achieved through the integration of the spring function into one of the two components of the valve and through the avoidance of the need to use an individual coil spring, which is achieved hereby, but rather the operational reliability is increased and the handling made easier.
The central body is of substantially cylindrical shape and has a diameter of approximately 1 mm to 10 mm, and the diameter of the central body is approximately 0.01 mm to 2 mm smaller having a valve diameter in in comparison to the diameter of the venting bore. It can be fixed by clamping elements which are provided on the central body or on the sealing part in the respective venting bore, while forming air passages. Depending on the arrangement of the clamping elements on the central body or on the sealing part, two different embodiments of venting valves arise which are, however, equivalent with respect to their function. Since they each only consist of two parts, an adequately large air throughflow cross-section is present and closing and opening procedures take place in a predeterminable and reliable manner as a result of the defined spring force.
Valves formed in accordance with the invention the range from about 2 mm to 12 mm can be manufactured of the most diverse materials, in particular of sheet metal spring material, die-cast aluminium or zinc, ceramic, sintered metals and also of injection-moulded parts of appropriately suited metals or corresponding temperature-resistant plastics.